You have what is described as an isthmic spondylolisthesis- grade II at L5-S1 with a concomitant mild degenerative disc at L4-5. Please read the extensive information regarding this on the website.
The slip amount at L5-S1 is larger than “normal” (Grade I) and this is why it probably creates more pain. Pain can be back pain and instability or leg pain or both. The leg pain would initially be caused by standing and walking and relieved by bending forward and sitting. After further degenerative changes, this leg pain could wake you up at night.
If you could respond to therapy and epidural injections, that would be the next step as long as you have not developed motor weakness.
The repair is the “blue plate special” (if you are old enough to remember that), a very common surgical repair. The surgery is called a TLIF with a Gill procedure and can eliminate pain and restore function. You can find a description of that surgery on the website.
Dr. Corenman